Microwave induced functionalization of single wall carbon nanotubes and composites prepared therefrom

ABSTRACT

The invention is directed to a method of forming, producing or manufacturing functionalized nanomaterials, and, specifically, soluble functionalized nanomaterials. The presently described invention also relates to nanomaterial-based composites consisting of a target material, which can include ceramic, polymer, or metallic matrices incorporated into or grown on nanomaterials, as well as a method or synthesis technique for the formation, production, or manufacture of nanomaterial-based composites through microwave-induced reaction.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.60/660,802 filed Mar. 11, 2005; U.S. Provisional Application No.60/767,564 filed Jan. 10, 2006; and U.S. Provisional Application No.60/767,565 filed Jan. 10, 2006, all of which are herein incorporated intheir entirety.

FIELD OF THE INVENTION

The present invention relates to the field of nanomaterials, includingsingle wall nanotubes (SWNTs), multiwall nanotubes, nanohorns,fullerenes, nano onions, and nanocomposites. More particularly, thepresent invention relates to a method of forming, producing ormanufacturing functionalized nanomaterials, and, specifically, solublenanomaterials. The presently described invention also relates tonanomaterial-based composites consisting of a target material, which caninclude ceramic, polymer, or metallic matrices incorporated intonanomaterials, as well as a method or synthesis technique for theformation, production, or manufacture of nanocarbon composites throughmicrowave-induced reaction.

BACKGROUND OF THE INVENTION

Single Wall Nanotubes (SWNTs)

There has been an intense interest in carbon nanotubes (CNTs) sincetheir discovery by Iijima in 1991, in large part because they possessunique structural and electronic properties. Single wall carbonnanotubes (SWNTs) are the fundamental form of carbon nanotubes withunique electronic properties that emerge due to their onedimensionality. An SWNT comprises a single hexagonal layer of carbonatoms (a graphene sheet) that has been rolled up to form a seamlesscylinder. Three types of SWNTs with differing chirality are expected toopen new frontiers with applications ranging from new materials, toelectronics and molecular scale sensing. Several processes for largescale synthesis/manufacture of SWNTs are also being developed by variousresearch groups around the globe. These include Laser ablation (PLV)reported by Smalley's and Eklund's group (Guo et al., Chem Phys Lett.,243 (1995) 49; Eklund et al., Nano Letters (2002), 2(6), 561-566), arcdischarge by Journet and coworkers (Journet et al., Nature (London)(1997), 388 (6644), 756-758) and chemical vapor deposition (CVD) methodby several different groups (Nikolav et al., Chem. Phys. Lett., 313(1999) 91; Wang et al., Chem. Phys. Lett., 364 (2002) 568-572; Kato etal., Thin Solid Films, 457 (2004) 2-6; Lyu et al., J. Phys. Chem. B,(2004), 108, 1613-1616). CVD methods include high pressure and catalyticCVD. SWNTs produced from different methods show slight variations intheir electronic properties, and in size distribution (Kuzmany et al.,Synthetic Metals, 141 (2004) 113-122). (All references cited in thisparagraph are herein incorporated by reference in their entirety).

Functionalization of SWNTs has been of much interest to the scientificcommunity because it enhances applicability. For example, insolubleSWNTs can be rendered soluble, which will lead to easy processibility,as working with a suspension is always a challenge. Functionalizationmay also lead to more efficient purification/separation techniques, suchas, those based on chirality, or, the separation of metallic SWNTs fromsemi-conducting ones. More importantly, functionalization leads to thedevelopment of new classes of material with specificity for differentphysical and chemical properties.

SWNTs have no functional groups and are consequently quite inert.Limited reactivity arises due to the curvature induced stress from thenon-planer sp² carbons and the misaligned n orbitals. While there is awealth of literature on the derivatization of the SWNTs, the two mostgeneral approaches appear to be 1,3-dipolar cycloaddition, and oxidationof some of the atoms at the tube ends or on the tube wall, and thensubstitution of the functionality thus formed (—F, —OH, —COOH). At thispoint, a variety of synthetic organic reactions can be carried out. Anexample of the former approach is a reaction with azomethine. The latterapproach, on the other hand, requires a more aggressive oxidation, suchas, refluxing with HNO₃, ozonation, or reaction with solid KOH.

Much of the effort so far has involved the use of conventionaltechniques such as refluxing and sonication. For differentfunctionalization purposes, carbon nanotubes are usually treated indifferent solvents by refluxing, or heating and stirring. Many of thesereactions need to be carried out over a long period of time. Forexample, for generating carboxyl groups, carbon nanotubes are oftenrefluxed in concentrated HNO₃ for tens of hours; thereafter, severaldays are required for refluxing (or heating) for furtherfunctionalization in processes such as acyl chlorination and amidation,diimide-activated amidation, or 1,3-dipolar cycloaddition.

Acid treatment has been the most commonly used functionalizationapproach. It leads to debundling of the nanotubes, and is the first steptowards amidation, esterification and other applications. Conventionalacid treatment is a long process, however, as it requires several hoursto several days depending upon the requirements of the final product.Further, most of the reported methods also involve multiple steps, andonly a limited solubility has been achieved (order of few milligrams perliter) (see for example, Loupy A. Solvent-free microwave organicsynthesis as an efficient procedure for green chemistry, C. R. Chimie(2004) 7(2): 103-112; Lewis et al., Accelerated imidization reactionsusing microwave radiation, J. Polym. Sci. A (1992) 30:1647-1653). Thedevelopment of a fast, efficient and controllable technique for SWNTfunctionalization will dramatically speed-up their real worldapplications.

A key issue in functionalization of SWNTs has been the desire toincrease their solubility in both water and organic solvents. Onedisadvantage of many nanomaterials is their limited solubility in commonsolvents. Solubility of nanomaterials, specifically carbon nanotubes, inwater would allow chemical derivatization and manipulation of thenanotubes to be facilitated simply and less expensively. Due to thetremendous benefits that soluble nanomaterials would create,considerable efforts have therefore been made in the past to make carbonnanotubes soluble in water and in organic solvents, but to date havebeen met with only limited success. Moreover, the solubilities achievedare mostly due to water-soluble macromolecules attached to thenanotubes, rather than the development of a soluble nanomaterial.

Microwaves

Microwaves are electromagnetic radiation in the 0.3-300 GHz frequencyrange (corresponding to 0.1-100 cm wavelength). To avoid interferencewith communication networks, all microwave heaters (domestic orscientific) are designed to work at either 2.45 GHz or 0.9 GHz, ofwhich, the former is more prevalent. According to Planck's law, theenergy at this wavelength is 0.3 cal/mol, and is therefore insufficientfor molecular excitation, thus most of the energy is used in substrateheat-up. The mechanism of microwave heating is different from that ofconventional heating, where heat is transferred by conduction,convection or radiation. In microwave heating, electromagnetic energy istransformed into heat through ionic conduction and the friction due torapid reorientation of the dipoles under microwave radiation. The largerthe dipole moment of a molecule, the more vigorous is the oscillation inthe microwave field, consequently more heating. This type of heating isfast, has no inertia, and is in-situ without heating the surroundings.

Chemistry under microwave radiation is known to be quite different, fastand efficient (Gedye et al., Tetrahedron Lett., 27 (1986) 279; Giguereet al., Tetrahedron Lett., 27 (1986) 4945; Loupy et al., Chimie, 7(2004) 103-112). It also reduces the need for solvents, thus it iseco-friendly. It has been exploited in a variety of organics synthesisincluding hetero cyclic, organometallic, and combinatorial chemistry.Some of the reported advantages are rapid reactions under controlledtemperature and pressure (especially in a closed system), higher purityproducts achieved due to short residence times at higher temperatures,and better yields at even very short residence times. Another importantfactor is that during dipolar polarization under microwave radiation,the activation parameters are modified. For example, it has beenreported by Lewis that during imidization of polyamic acid, theactivation energy reduced from 105 to 57 KJ/mol. (Lewis et al., J.Polym. Sci., 30A (1992) 1647) (All referenced cited in this paragraphare herein incorporated by reference in their entirety)

Composites

The mechanical properties of single wall carbon nanotubes (SWNTs) suchas their stiffness, elasticity and high Young's modulus, make them idealcandidates for structural reinforcements in the fabrication of highstrength, light weight, and high performance composites. Considerableinvestigations have been conducted on the SWNT based composites by boththeoretical and experimental means. These prior art approaches involve,among other things, dispersion, melt mixing, milling, covalent graftingor in-situ growing SWNTs in different polymer or ceramic matrix toachieve the certain composite. The results, however, conflict amongstudies wherein some studies revealed that the introduction of SWNTs inpolymer clearly enhances both the physical and mechanical propertieswhile others showed that the carbon nanotube contributed no mechanicalimprovement to the composites.

The ineffective utilization of nanotubes as reinforcement in compositesis normally suffered from two factors, non-uniform dispersion of SWNTsin matrix and poor interfacial bonding between them. The latter oneconsequently will result in low efficiency of load transfer across thenanotube/matrix interface, and the pull-out of carbon nanotubes from thematrix can be observed when the composites are under extension.

The excellent mechanical, thermal and electrical properties of carbonnanotubes and SWNTs would be significantly enhanced by the developmentof nanocomposites containing ceramic, polymer and metal incorporatedinto carbon nanotubes. Desirable properties for ceramic, polymer andmetal composites include mechanical toughness, wear resistance, and thereduction in crack growth coupled with improved thermal conductivity,resistance to thermal shock and increased electrical conductance. Forexample, the ceramics are inherently brittle and the incorporation ofSWNTs is known to have improved toughness by as much as 24% (Kamalakaranet al., Microstructural characterization of C-SiC-carbon nanotubecomposite flakes, Carbon (2004) 42(1): 1-4).

Significant efforts have gone into theoretical and experimentalinvestigations of carbon nanotube-based composites, but challenges infabrication, particularly for ceramics and metals have not beenovercome. Fabrication methods such as, hot pressing, sintering, milling,covalent grafting and in-situ catalytic growth in ceramic and polymermatrices via chemical vapor deposition (CVD), have been used. Thesemethods may be classified as those where the carbon nanotubes and theceramic were physically mixed and then bonded by heat-treatment, orthose where the nanotubes were grown in a ceramic matrix via CVD. Thistypically generates a mixture of single and multiwall nanotubes alongwith amorphous carbon. As an example of the former approach,Al₂O₃/nanotube composites were prepared by ball milling a methanolsuspension of the ceramic and nanotubes for 24 hours (Wang et al.,Contact-damage-resistant ceramic/single-wall carbon nanotubes andceramic/graphic composites, Nature Materials (2004) 3: 539-544). Anexample of the latter is the synthesis from a slurry of SiC andferrocene in xylene, which was sprayed into a reactor at 1000° C. underargon (Kamalakaran et al.). The observed ineffective utilization ofcarbon nanotubes as the reinforcing material in many of these compositeshas been attributed to the non-uniform dispersion of carbon nanotubes,and the poor interfacial adhesion to the matrix. For example, the latterresults in ineffective load transfer across the nanotube/matrixinterface, and the “pullout” of carbon nanotubes has been observed whenthe composite is under strain. An important issue has been the hightemperature and reactivity of some of the current methodologies, whichcan destroy and/or damage the carbon nanotubes.

In summary, functionalization of carbon nanotubes by known conventionalmethods is a tedious and time-consuming procedure. Consequently, thereis a need to develop techniques for fast functionalization andsolubilization of SWNTs, as well as composites thereof.

SUMMARY OF THE INVENTION

The present invention is directed to a method for rapidlyfunctionalizing a nanomaterial, comprising performing afunctionalization reaction wherein said functionalization reactioncomprises subjecting said nanomaterial and at least one functionalizingreactant to microwave conditions.

The invention is further directed to a method for rapidly generating asoluble, functionalized nanomaterial comprising a functionalizationreaction wherein said functionalization reaction comprises subjectingsaid non nanomaterial and at least one functionalizing reactant tomicrowave conditions.

The invention is also directed to a method for producing a nanomaterialcomposite comprising the step of growing a ceramic on a nanomaterial.

The invention is even further directed to a method for producing ananomaterial composite comprising the step of growing or polymerizingtarget material precursors on the nanomaterial.

The invention additionally is directed to a method for synthesizing ananomaterial composite comprising:

-   -   providing a nanomaterial;    -   adding a target material selected from the group consisting of a        ceramic compound, a metal, a polymer, and combinations thereof,        to said nanomaterial, wherein the target material and        nanomaterial combination is exposed to microwave conditions to        form said nanomaterial composite.

The invention is finally directed to a method for synthesizing ananomaterial composite comprising of decomposing a metal salt or anorganometallic compound on the nanomaterial.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 compares the FTIR spectra of (a) pristine SWNTs, (b) HNO₃ treatedSWNTs with microwave, and (c) 2,6-dinitroaniline functionalized SWNTs.

FIG. 2 compares the Raman spectra of (a) pristine SWNTs and (b)2,6-dinitroanaline functionalized SWNTs.

FIG. 3 compares the FTIR spectra of (a) L-methionene, (b)salicylaldehyde, and (c) final product of 1,3-dipolar cycloaddition ofSWNTs.

FIG. 4 (a) shows the UV-vis absorption spectroscopy of the mixture ofstarting material.

FIG. 4 (b) shows the UV-vis absorption spectroscopy of the final productof 1,3-dipolar cycloaddition of SWNTs

FIG. 5 presents the H NMR of the final product of 1,3-dipolarcycloaddition of SWNTs

FIG. 6 sets forth SEM images of (a) pristine SWNTs; (b) same pristineSWNTs at higher magnification; (c) SWNTs after 1,3-dipolar cycloadditionfunctionalizaton; and (d) same SWNTs after 1,3-dipolar cycloadditionfunctionalizaton at higher magnification.

FIG. 7 consists of a series of photographs of SWNTs solution indistilled water as follows: (a) 0.05 mg/ml, (b) 0.1 mg/ml, (c) 0.2mg/ml, (d) 0.3 mg/ml, (e) 0.5 mg/ml and (f) 2 mg/ml.

FIG. 8 (a) depicts SEM images of functionalized SWNTs deposited from anaqueous solution wherein the bottom image depicts the SEM image at lowermagnification showing alignment of the functionalized SWNTs (scale bar=2μm) and the top image is a higher magnification image of the alignedSWNTs (scale bar=200 nm).

FIG. 8 (b) depicts a TEM image of functionalized SWNTs deposited from anaqueous solution specifically showing debundled functionalized SWNTs(scale bar=10 nm).

FIG. 9 (a) depicts FTIR spectra (excited by 632.8 nm radiation) of thefunctionalized SWNTs, wherein (a) pristine SWNTs; and (b) microwavefunctionalized SWNTs.

FIG. 9 (b) depicts Raman spectra (excited by 632.8 nm radiation) of thefunctionalized SWNTs wherein (a) pristine SWNTs; (b) functionalizedSWNTs in solid phase, and (c) functionalized SWNTs in aqueous solution.

FIG. 10 (a) depicts visible-near infrared (vis-NIR) spectra data underpure nitrogen at a heating rate of 10° C. per minute for pristine andmicrowave functionalized SWNTs, wherein (a) Pristine SWNTs suspended indimethylformamide, and (b) Aqueous solution of microwave reactednanotubes.

FIG. 10 (b) depicts thermogravimetric analysis (TGA) data under purenitrogen at a heating rate of 10° C. per minute for pristine andmicrowave functionalized SWNTs, wherein (c) pristine SWNT powder and (d)microwave functionalized SWNTs.

FIG. 11 comprises optical images of the SWNTs and SiC composite rapidlyprecipitating out of the fine suspension. FIG. 11 a depicts the wholecomposite at a scale bar of 1 cm. FIG. 11 b is a magnified portion ofthe composite shown at a scale bar of 2 mm.

FIG. 12 shows an X-ray diffraction (XRD) pattern of the face-centeredcubic structure of the SiC component in the SiC-SWNT composite.

FIG. 13 shows FTIR spectra of the materials in the reaction process usedto create the composite at various stages of the process. FIG. 13 (a)depicts the purified and acid washed SWNTs. FIG. 13 (b) depicts startingmaterial of chlorotrimethyl silane. FIG. 13 (c) depicts the SWNTs-SiCcomposite. The “*” in FIGS. 13 (a) and 13 (c) denotes the water impurityfrom KBr used as a supporting matrix for the samples.

FIG. 14 depicts the Raman spectra of the SWNT composites in a pristineform and as-reacted with SiC. FIG. 14 (a) depicts the spectrum ofpristine SWNTs, while FIG. 14 (b) depicts the spectrum of the SiC-SWNTcomposite.

FIG. 15 depicts SEM and TEM images of the SWNTs-SiC composite. FIG. 15(a) depicts the SEM image of SWNTs covered by fine SiC particles at ascale bar of 200 nm. FIG. 15 (b) depicts a SEM image showing anindividual nanotube covered by SiC particles at a scale bar of 200 nm.FIG. 15 (c) depicts a SEM image showing a portion of SWNTs fully coveredby SiC spheres at a scale bar of 200 nm. FIG. 15 (d) depicts a SEM imageshowing embedded nanotubes from the fractured composite at a scale barof 1 μm. FIG. 15 (e) depicts a TEM image of debundled, SiC coated SWNTs,and randomly linked by SiC spheres at a scale bar of 50 nm. FIG. 15 (f)depicts a magnified TEM image showing the SiC coated and linkednanotubes at a scale bar of 10 nm.

FIG. 16 (a) depicts the mechanism for growth of the SiC-SWNT composite.

FIG. 16 (b) is a pictorial illustration of the linkage between SiC andSWNTs.

FIG. 17 depicts carbon nanotubes coated by solid phase LiAlH₄decomposition.

FIG. 18 depicts the energy dispersive x-ray (EDX) spectra of carbonnanotubes coated with LiAlH₄ decomposition.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is a method of forming, producing or manufacturingrapidly functionalized and highly soluble nanomaterials, mostspecifically carbon nanotubes. Specifically, we present the firstapplication of microwave-induced functionalization of Single wallnanotubes (SWNTs), which reduces the reaction time to the order ofminutes.

For the purposes of this application “nanomaterials” can include singlewall nanotubes (SWNTs), multiwall nanotubes, nanohorns, fullerenes, nanoonions and nanocomposites. These nanomaterial also include but are notlimited to carbon based nanomaterial such as carbon nanotubes and carbonSWNTs.

Functionalization of nanomaterials serves several important functions.Materials such as carbon nanotubes are inert and do not mix and blendeasily in most matrices. They are not soluble either, so they can not beprocessed easily either in thin films or polymer composites.Functionalization allows the chemical structure of the nanotubes to bemodified, and other functional groups, polymers, ceramics, biologicalmolecules such as enzymes and other appropriate chemical moeties can beattached. For example treating with acid generates —COOH groups to whichother functionalities can be attached by a variety of chemicalreactions. Some functionalization reactions may be carboxylation,sulfonation, esterification, thiolation, carbine addition, nitration,nucleophylic cyclopropanation, bromination, fluorination, diels alderreaction, amidation, cycloaddition, polymerization, adsorption ofpolymers, addition of biological molecules and enzymes etc. Thefuntionalization may be covalent bonding to the nanotube, or noncovalentadsorption or wrapping. By putting appropriate functionality, thenanotubes may be rendered soluble in aqueous, organic, polar, nonpolar,hydrogen bonding, ionic liquids, and other solvents so that they can beprocessed easily. Polymer or ceramic precursor may also be reacted withnanotubes to form composites, or biological molecules may be attachedfor drug delivery, sensing or other important functions.

In general, the process of the invention begins with the combining ofthe desired nanomaterial, either prefunctionalized ornon-functionalized, with the functionalizing reactant such as an acid,base, urea, alcohol, organic solvent, benzene, acetone and any otherreactant that achieves the desired functionalization reaction. Thecombination is then subjected to appropriate microwave conditions thatresult in functionalization of the nanomaterial. In alternativeembodiments, the functionalized nanomaterial can be subjected to furtherfunctionalization reactions using the same inventive process. Forexample, it may be necessary to functionalize a nanomaterial withcarboxyl groups prior to functionalizing with desired functionalizingreactant.

The method of the invention incorporates the use of microwave inducedfunctionalization of SWNTs. This high-energy procedure to reduce thereaction time to the order of minutes. The microwave provides in-situ,molecular heating in a microwave oven. The power and time can beadjusted for optimized performance and results. Specifically, themicrowave power is adjustable anywhere from a few hundred watts toseveral kilowatts depending upon how quickly one desires the reaction tobe completed. Such conditions will vary depending upon the desiredfunctionalization reaction. Preferred reaction times forfunctionalization are anywhere from 1 second to 30 minutes. The amountof material to be processed can range anywhere from a few mg to severalkg, . . . .

Two preferred embodiments include amidation of SWNTs and 1,3-dipolarcycloaddition of SWNTs. The amidation reaction is completed in two steps(as opposed to three in conventional approaches). Specifically, whilethe step involving acyl chlorination is bypassed, the yield remains thesame. The 1,3-dipolar cycloaddtion of SWNTs embodiment can be carriedout in, for example, 15 minutes under microwave conditions, and theresults are similar to what was achieved in 5 days using conventionalmethods. In summary, microwave assisted reactions are a fast andeffective method for reactions involving SWNTs.

The first preferred embodiment involves carboxylation (generation of—COOH) of SWNTs followed by amidation, as shown in the scheme 1 below.

-   -   Scheme 1, amidation of SWNTs,

The second preferred embodiment is 1,3-dipolar cycloaddtion reaction ofSWNTs, together with α-amino acid and aldehyde, and this is shown asscheme 2 below.

-   -   Scheme 2, 1, 3-dipolar cycloaddition of SWNTs,

A distinct advantage of the present invention is rapid funtionalization.The speed of this reaction is partially due to rapid heating and evensuperheating at a molecular level. Side reactions are also eliminated asthe bulk does not need to be heated. When practicing the disclosedmethod of synthesis, the microwave induced reaction occurs in a matterof seconds or minutes and can generate a high purity product with highyield. This is advantageous because it makes the overall process costeffective.

Further, the microwave induced reactions as a means of nanotubefunctionalization is also extremely important from the stand point ofprocess development and scale-up. The ease of creating functionalizedsoluble nanomaterials increases production of nanomaterials at a reducedprice thereby enabling sufficient quantities to be produced for use incommercial goods as well as production at a cost that can be toleratedby consumer markets. Additionally the method in generally reducesreaction time by orders of magnitude and provides high yield adding toits cost effectiveness.

Also presented in this document is a novel, simple and fast approach tosynthesize highly water soluble nanomaterials under microwave radiation.Carbon nanotubes, for example, have inert, graphitic sidewalls and aretherefore extremely insoluble in common solvents. In order to makecarbon nanotubes soluble in water and related organic solvents commonlyused in chemical and biological applications, a new method to producehighly effective and rapid sidewall functionalization was required andis presently disclosed.

One embodiment of the present invention is a method for generatingsoluble nanomaterials by the use of microwaves and an acidicenvironment. The acidic environment can be a suspension of nanotubes inan acid or acid mixture. In one embodiment, a blend of acids, in avariety of proportions can be used to create the acidic environment. Byway of example only and without limitation, some examples of acids thatcould be utilized to create the acidic environment include, nitric acid,sulfuric acid, hydrochloric acid, as well as other organic and inorganicacids. In one embodiment, a pairing of nitric acid and sulfuric acid canbe used to create the acid treatment. In another embodiment a 1:1mixture of concentrated nitric acid and sulfuric acid in water was used.

This embodiment is an environmentally friendly, microwave-induced methodto prepare highly water-soluble single-walled nanotubes (SWNTs) in aboutthree minutes, using a closed vessel reactor. This embodiment hasgenerated measured solubilities of more than 10 mg of nanotubes permilliliter of water and ethanol, which is several orders of magnitudehigher than what has previously been achieved in the art. Additionallythe solutions were free of suspended nanotubes as determined by lightscattering measurements, and for the first time Raman spectrum of SWNTswas obtained from its solution phase.

In one illustrative embodiment of the method currently described, highlypure single wall carbon nanotubes (SWNTs), were suspended in a 1:1mixture of concentrated nitric acid and sulfuric acid in water andreacted in a closed vessel microwave oven for less than five minutes.Functionalized SWNTs obtained after three minutes of microwave treatmentwere found to have solubilities of more than 10 mg of SWNTs permilliliter of de-ionized water and ethanol under ambient conditions, andsignificantly higher solubilities were obtained in acidic water.Photographs of aqueous solutions of different concentrations offunctionalized SWNTs produced by this method are shown in FIG. 7. Thepresently disclosed method, as seen through this particular embodiment,is a relatively simple microwave technique that produces highlywater-soluble nanotubes that enable the processing of nanotubes in bulkquantities and hasten real-world applications of this unique material.

In the current invention, the placing of a nanomaterial in an acidicenvironment maybe called an acid treatment. In one embodiment, when thenanotubes contact the acid treatment, the nanotubes became nitrated.

The presently described method offers the significant advantages ofgenerating high solubility functionalized nanomaterials that are rapidlyfunctionalized at low temperatures with preferred alignment in solutionand electrically conductive properties. Additionally, the method itselfis environmentally friendly and scalable for industry thereby enablingthe production of economical bulk quantities of highly reproducibleproduct to consumers.

Specifically, the method of the present disclosure offers significantadvantages relative to prior art. The advantageous properties and/orcharacteristics of the disclosed method include, but are not limited to,high solubility functionalized nanomaterials, preferred alignment of thenanomaterials in solution, rapidly functionalized nanomaterials,electrically conducting nanomaterials, environmentally friendly,scalable for industry to produce bulk quantities and economically bringthe product to consumers, it generates highly reproducible products andcan operate at low temperatures.

The resultant high water and alcohol solubility of the method of theinvention will enable nanomaterials and SWNTs to be more easilyprocessed in operations involving chemical reactions, physical blending,or thin film formation. Further, the nanomaterials and SWNT will have amore preferable alignment during deposition from solution due to thepresently disclosed method. The enhanced alignment will facilitate thecreation of novel nanoelectronic device architectures.

The resulting soluble nanomaterials of the invention can also beelectrically conducting. The SWNT can display significantly higherconductivity in de-ionized water, for example, in this case as high as215.8 μS (one or two orders of magnitude higher is also possible)relative to that of 1.5 μS for de-ionized water. This advantage raisesthe possibility for electrical manipulation (such as, electrodeposition)of the SWNTs from a solution phase.

The presently disclosed method of synthesis is also highly reproducibleas evidenced by the creation of a solid composite of similar morphology,shape, and color with every reaction (see Example 3). The high level ofreproducibility is partially due to the controlled environment. This isadvantageous because high purity products can be obtained.

The presently disclosed method of synthesis is appealing because itrequires a relatively low temperature microwave-induced reaction toproduce soluble nanomaterials. The presently disclosed method ofsynthesis has the ability to operate at a low temperature due in part toin-situ heating at the reaction site. This is advantageous because itleads to fast reaction kinetics and reactions that would not otherwisebe possible.

COMPOSITES OF THE INVENTION

The present invention is also directed to a composite consisting oftarget material(s) such as ceramic, polymer or metals to be incorporatedinto or grown on nanomaterials such as carbon nanotubes or SWNTs.Specifically, the present invention provides a technique for theformation, production, or manufacture of nanomaterial composites througha controllable, rapid, relatively low temperature microwave-inducedreaction. In one embodiment, the process of the invention comprises thecombination of a target material precursor with the desired nanomaterialunder microwave conditions such that the target material forms on thenanomaterial (e.g. polymerization).

In the process of the invention, appropriate quantities of the targetmaterial and the nanomaterial are blended or mixed together under knownconditions and are then subjected to appropriate microwave conditions toform the desired composite. In an alternative embodiment, a precursor tothe target material is combined with the nanomaterial under knownconditions, and said combination is subjected to appropriate microwaveconditions that induce formation of the target material from theprecursor which then combines with the nanomaterial to form the desiredcomposite. More specifically, a reaction can be carried out to depositceramic or polymer material on the nanotube. The other approach is thatpolymer or ceramic precursors can be polymerized or synthesized directlyon the nanotube sidewalls.

Often times it may be necessary to functionalize the nanomaterial priorto forming the composite. It is contemplated herein that thefunctionalization of the nanomaterial be accomplished using the methodof this invention prior to subjecting the nanomaterial to the compositeformation set forth in the invention.

Some examples of ceramic compounds that are suitable for use in theinvention include, but are not limited to, carbides, borides, nitrides,silicides, barium titanate, bismuth strontium calcium copper oxide,boron carbide, boron nitride, aluminum silicates, earthenware, Ferrite,lead zirconate titanate, magnesium diboride, porcelain, silicon carbide,silicon nitride, Steatite, uranium oxide, yttrium barium copper oxide,zinc oxide, zirconia, and combinations thereof.

In a preferred embodiment, some examples of metals suitable for use inthe invention include salt such as LiAlH4. LiBH4; and CdS.

Some examples of preferred polymers, and precursors thereof, include,but are not limited to methyl methacrylate, polyvinyl pyrrolidone,polyurethane, polyamide and any other related polymers.

In particular, the process of the invention is excellent for creatingnovel nanoscale silicon carbide (SiC)-carbon nanotube composites andmetal-nanotube composites. More particularly, the present inventionrelates to a method enabling the formation of a ceramic or polymerdirectly on the carbon nanotubes, rather than physical mixing, or thegrowth of nanotubes in a ceramic or polymer matrix. The describedtechnique creates mechanical toughness, wear resistance, and thereduction in crack growth coupled with improved thermal conductivity,resistance to thermal shock and increased electrical conductance.

In particular, the process is excellent for using a variety of silanolcompounds, including silicon carbide (SiC), to create novel nanoscalecomposites such as silicon carbide (SiC)-carbon nanotubes, and, moregenerally, metal-nanotube composites. Silicon carbide (SiC) is aninteresting material because it can be used for high-temperature andhigh-power electronic applications due to its excellent properties, suchas high mechanical strength, high thermal stability, high thermalconductivity and large band gap. In addition, nanometer size SiCnanostructure might hold novel chemical and physical properties forfabricating electronic nanodevices.

A preferred embodiment includes a novel, low temperature,microwave-induced approach for the synthesis of a high purity SiC-SWNTcomposite. The reaction of the invention can be completed in a matter ofminutes, and involves the nucleation of SiC directly on the SWNTbundles. In the prior art, formation of multiwalled tubes and othercarbonaceous structures is usually performed in the reverse of whatoccurs in the present invention, i.e. growth of SWNTs in a ceramicmatrix does not occur in the process of the invention because theprocess begins with the use of highly purified SWNTs. Specifically, thereaction involves the pyrolysis of the chlorotrimethylsilane andsimultaneous nucleation of nanoscale SiC spheres onto carbon nanotubes.This reaction was carried out in microwave, and the whole processinvolves one step and about 10 min. In our testing, we randomly crossedlinked the obtained composite into a root like structure (Shown in FIG.11). The SiC-SWNT composite was analyzed and confirmed by X-raydiffraction (XRD), transmission electron microscope (TEM), scanningelectron microscope (SEM), energy dispersion X-ray (EDX), Raman andfourier transform infrared (FTIR) spectra (see Example 3).

Regarding the above SiC-nanocarbon composite, we found stronginterfacial bonding was indicated between nanometer size SiC spheres andSWNTs. This new material may thus open the door for fabricatingnanoscale electronic devices.

An alternative embodiment of the invention relates to the synthesis of aceramic carbon nanotube composite which incorporates ceramic matricesinto carbon nanotubes. One specific embodiment of the invention is aceramic SWNT composite, which incorporates ceramic matrices into SWNTs.Examples of these embodiments are illustrated in FIGS. 12-15. Thepresent invention includes but is not limited to nanotubes, nanohorns,graphite and all similar or related structures.

In the method of synthesis of a ceramic SWNT, a preferred embodimentinvolves utilizing a microwave oven and a reaction chamber, lined withTeflon PFA® and fitted with a pressure controller. The SWNTs are firsttreated with a solution having acidic properties, such as nitric acid,sulfuric acid, and any other suitable organic and inorganic acid, for ashort period of time under microwave conditions to reduce or eliminateresidual metal catalyst and generate carboxyl groups. A silinol or apolymer precursor compound (e.g., methyl methacrylate), which containsthe desired base material necessary to create the compound, is utilized.Then pretreated SWNTs and the precursor compound are added to themicrowave reaction vessel and subjected to microwave induced reactionwhile controlling time, power (wattage) and pressure. The silanolprecursor decomposes and the polymer precursor polymerizes to form saidcompound. The liquid in the control vessel is cooled and is then removedfrom the reaction chamber, washed and then dried.

More specifically, in this embodiment, the method of synthesis of theceramic SWNTs presently described preferably involves the utilization ofa microwave oven and a Teflon PFA® lined reaction chamber fitted with apressure controller. The SWNTs are treated in the microwave with anitric acid solution. The pretreated SWNTs are then added, along withchlorotrimethylsilane to the microwave reaction vessel and subjected tomicrowave induced reaction while controlling time, power (wattage) andpressure, thereby synthesizing the ceramic SWNT composites presentlydisclosed (see Example 3 for more detail).

In another embodiment of the method of synthesis of the ceramic,polymer, metallic or carbon nanotubes, the composite has been grown onthe nanotubes by decomposing a chemical. In one embodiment, the reactioninvolves the microwave-induced decomposition of chlorotrimethylsilane inthe presence of carbon nanotubes. Chlorotrimethylsilane provides an easyto decompose source of silicon for in-situ forming of the SiC componentof the composite.

More specifically, the reaction involves the microwave-induceddecomposition of a precursor chemical in the presence of carbonnanotubes, such that the new formed nanocarbon composite is formeddirectly around the tube. Accordingly, interfacial bonding is improvedby in-situ growth of the ceramic or polymer or metal on the carbonnanotubes as opposed to the methods described in the prior art wherebythe interfacial bonding occurs by adding the carbon nanotubes onto apre-prepared ceramic or polymer. The presently disclosed compositeformed in accordance with the disclosed method of a controllable rapid,relatively low temperature microwave-induced interfacial bondingsignificantly increases the mechanical toughness, wear resistance,thermal conductivity, resistance to thermal shock, and electricalconductance while reducing crack growth.

In another embodiment, the nanotube-metal composites can be fabricatedby reactive processes. Reaction with a metal salt or a complex can becarried out. By way of example only and without limitation, an exampleis the reaction with lithium aluminum hydride (LiAlH4). The solid phasereaction of the nanotubes and LiAlH4 was carried out in an oven attemperature 250° C. or for a few minutes in a microwave. The LiAlH4powder decomposed according to:LiAlH4⇄LiH+Al+3/2H2  (1)

Some of the Al is then deposited on the nanotube surface. The SEM imageof Al coated nanotubes obtained by LiAlH4 decomposition is shown in FIG.17, which shows the thickness of deposited Al. The typical EDX spectraof nanotubes coated with Al by LiAlH4 decomposition is shown in FIG. 18.

In alternate embodiments, the ceramic element can be substituted for bya polymer thereby creating a polymer nanomaterial composite or a metalthereby creating a metal nanomaterial composite.

The composites of the present invention offer significant advantagesrelative to prior art. The advantageous properties and/orcharacteristics of the disclosed composite include, but are not limitedto, mechanical toughness, wear resistance, reduction in crack growth,improved thermal conductivity and resistance to thermal shock, andelectrical conductance.

Regarding mechanical toughness, ceramics, for example are inherentlybrittle and the incorporation of nanotubes is reported to have improvedtoughness by as much as 24%. An increase in the mechanical toughness isa direct result of the improvement of the interfacial bonding caused bythe in-situ growth of the ceramic or polymer on the carbon nanotubes asopposed to the prior art whereby the carbon nanotubes is merely addedonto the pre-prepared ceramic. One benefit of mechanical toughness isthat it allows the carbon nanotubes to be used under more strenuousconditions.

Wear resistance is much like mechanical toughness and is attributable tothe improved interfacial bonding caused by the in-situ growth of theceramic on the carbon nanotubes rather than merely by adding the carbonnanotubes onto the pre-prepared ceramic, thereby extending the life ofthe carbon nanotubes in a variety of applications.

The method of synthesis of the invention further facilitates a reductionin crack growth which can be attributed to the high binding capabilitiesof the carbon nanotubes.

The method of synthesis of the composite of the present invention offerssignificant advantages relative to prior art. The advantageousproperties and/or characteristics of the disclosed method of synthesisof the composite includes, but are not limited to, rapid, lowtemperature microwave-induced reaction to create a novel nanoscalesilicon carbide (SiC)-SWNT composite without side reactions. The methodis highly reproducible by creating a solid composite of similarmorphology, shape, color was obtained every time, cost effective andenvironmentally safe. Additionally, the speed of the reaction can becontrolled. Finally, the in-situ heating facilitates reactions that areotherwise not possible.

The speed of the reaction is partially due to rapid heating and evensuperheating at a molecular level. Side reactions are also eliminated asthe bulk does not need to be heated. When practicing the disclosedmethod of synthesis the microwave induced reaction occurs in a matter ofseconds or minutes and can generate a high purity product with highyield. This is advantageous because it makes the overall process costeffective.

Because the method uses a relatively low temperature microwave-inducedreaction to create the novel composites, it is advantageous because itleads to fast reaction kinetics and reactions that would not otherwisebe possible. Also, the high level of reproducibility offered by theinvention is advantageous because high purity products can be obtained.Of course, the presently disclosed method of synthesis is cost effectiveas it reduces reaction time by orders of magnitude and provides highyield. Finally, the invention has great appeal due to it beingenvironmentally safe (minimal requirement of energy and chemicals).

Applicant has attempted to disclose all embodiments and applications ofthe disclosed subject matter that could be reasonably foreseen. However,there may be unforeseeable, insubstantial modifications that remain asequivalents. While the present invention has been described inconjunction with specific, exemplary embodiments thereof, it is evidentthat many alterations, modifications, and variations will be apparent tothose skilled in the art in light of the foregoing description withoutdeparting from the spirit or scope of the present disclosure.Accordingly, the present disclosure is intended to embrace all suchalterations, modifications, and variations of the above detaileddescription

EXAMPLES Example 1

Experiments were carried out in a CEM model_(—)205 microwave oven. Thereaction chamber was of 100 ml volume, lined with Teflon PFA®, andtilted with a 0˜200 PSI pressure controller.

For the amidation reaction, the first step was the generation ofcarboxylic acid groups on the SWNTS. In a typical application, 6˜10 mgof pristine SWNTs from Hipco process was loaded into an extractionvessel, along with 20 ml of conc. HNO₃ (70%). The microwave powersetting was 75% (total of 900 watts), the pressure was set at 125 PSI,and the reaction was carried out for 10˜15 min. After cooling the vesselto room temperature, the reacted mixture was filtered, washed and dried.About 5 mg of this carboxylic acid grafted SWNTs was used to react with2,6-dinitroaniline. On amidation reaction, 20 ml of DMF was used as thesolvent, 15 to 20 mg of amine was added, and all other conditionsremained same as before. The reaction was carried out for 15 to 20 min.Once cooled, the mixture was filtered, washed with DMF and anhydrousTHF. After vacuum drying at room temperature for few hours, the samplewas analyzed by FTIR and Raman spectroscopy.

For the 1,3-dipolar cycloaddition reaction, about 10 mg of pristineSWNTs and 70 mg of salicylaldehyde were suspended in 20 ml DMF. Then,the mixture was heated in the microwave for 5 min at 90% microwavepower, and at pressure setting of 160 PSI. After cooling, 2 ml ofmethionine suspension (70 mg in 4 ml) was added to the reaction vessel.Then reaction was carried out for 5 min at the same power and pressuresetting. Again the vessel was allowed to cool, and the other half of themethionine suspension was added, and the reaction was carried out foranother 5 min under the same conditions. Then, the reacted mixture wasfiltered, and the organic phase was vacuum evaporated. The resultingdark brown oil was extracted with CHCl3/H2O. Also, the organic phase waswashed with water for 5 times, and then dried with Na2SO4 over night.Then, it was evaporated, washed with ethyl ether, and around 7 mg ofdark brown solid was obtained after evaporation. The solid was evaluatedusing FTIR, H-NMR, SEM, and UV spectroscopy.

The conventional approach to amidation for SWNTs involves carboxylation,acyl chlorination, and amidation. It involves three steps and typicalreaction time is of 3 to 5 days. The amidation of SWNTS in a microwavewas a two steps process, and it's total reaction time is about 20 to 30min. SWNTs functionalized through amidation in microwave werecharacterized using FTIR and Raman spectroscopy. The results arepresented in FIGS. 1 and 2 respectively.

FIG. 1 shows the FTIR spectra of pristine SWNT (a), HNO₃ treated SWNT(b), and finally after 2,6-dinitroaniline functionalized SWNT (c). InFIG. 1 a, the peak at 1580 cm⁻¹ was assigned to C═C close to defect siteof nanotubes. The band at 1626 cm⁻¹ is water impurity from KBr used formaking the pellet, and this peak existed in FIGS. 1 b and 1 c as well.The C═O band at 1730 cm⁻¹ in the HNO₃ treated SWNT indicated successfulgeneration of COOH on the nanotubes (FIG. 1 b). The sharp peak at 1384cm⁻¹ is probably due to the nitration of NO₂ in SWNTS, which occurredduring the high pressure HNO₃ treatment in microwave. After the reactionwith 2,6-dinitroaniline, the amide linkage formed at the C═O as shown bythe absorption band at 1650 cm⁻¹ in FIG. 1 c. The remaining band at 1730cm⁻¹ indicated incomplete reaction due to the steric effect of rigidring from the attached amine.

The Raman measurements were carried out using a Horiba/Jobin YvonLabRaman system place with 632.8 nm excitation. The Raman spectroscopywas carried out on both pristine and functionalized SWNTs. The Ramanspectrum of functionalized SWNTs (FIG. 2 b) shows significantfluorescence, due to the coverage of the amine on wall or the ends ofSWNTs. Similar observation was also reported by several different groups(Huang et al., Nano. Lett., (2002) 2, 311; Lin et al., J. Phys Chem. B(2002), 106, 1294-1298; Ya-Ping et al., Acc. Chem. Res. (2002), 35,1096-1104). The enhanced peak at about 1330 cm-1 was attributed tocovalent modification, as it revealed sp³-hybridization of disorderwithin the nanotube framework.

Microwave Induced 1,3-Dipolar Cycloaddition of SWNT

1,3-dipolar cycloaddition of SWNT is a tedious and time consumingprocess when carried out by conventional methods, and may take as longas five days to complete the process. As mentioned above, the microwaveinduced reaction time was 20 to 30 min. The final product of 1,3-dipolarcycloaddtion functionalized SWNTs was highly soluble in CHCl₃ andCH₂Cl₂. It's FTIR spectrum, along with L-methionine and salicylaldehyde,is shown in FIG. 3.

The functionalized SWNTs (FIG. 3 c) shows the absence of the aldehydeC—H stretching peaks at 2749 cm⁻¹ and 2845 cm⁻¹, which were present inthe original aldehyde (FIG. 3 b). As shown in the detailed descriptionof this application, the aldehyde group was expected to be gone afterfunctionalization. Therefore the missing of the aldehyde C—H peaks inFIG. 3 c implies successful reaction of the functionalization. Thearomatic C—H stretching band in FIG. 3 c at 3052 cm⁻¹ was slightlyshifted, as compare to spectra 3 b of the aldehyde, which was at 3060cm⁻¹. Moreover, the peaks at 2917 cm⁻¹ and 2849 cm⁻¹ were from theattached amino acid. These peaks were absent in the FTIR spectra ofpristine SWNTs presented in FIG. 1 a. This clearly demonstrated thefunctionalization of SWNTs. Some strong peaks from the aldehyde and theamino acid remained and were reasonably shifted in the low wavenumberrange of the spectra.

UV-vis absorption analysis presented in FIG. 4 provided further evidenceof the functionalization reaction. The UV-vis absorption measurementswere made in CHCl₃. Spectra (a) is from the mixture of the startingmaterial taken in the same ratio as the reaction. It showed two broadabsorption bands at about 250 and 330 nm. After the reaction, two bandsremained, but shifted to the left, which was in agreement with theobservation of Prato et al (Prato et al., J. Am. Chem. Soc. (2002) 124,760-761). The shift of absorption bands provided further proof of achange in molecular structure brought by reaction.

The H NMR measurements were made with the 1,3-dipolar cycloaddtionproduct, and the results are shown in FIG. 5. These were carried out inCDCl3, and the solvent peak was shown at 7.27 ppm. The aromatic H formsalicylaldehyde still existed and are shown in the magnified window ofup-left corner, but the aldehyde H (CHO) disappeared from the chemicalshift at about 10 PPM. This is consistent with the FTIR measurements,and indicated that the reaction occurred. H from CH₃—S—CH₂— from theamino acid remained after the reaction, which is shown as the sharp peakat about 3.8 ppm. After reaction, and due to the lose of COOH group, thepeak of H close to original COOH group is slightly shifted to 1.9 ppmfrom 2.1 ppm (the H NMR of the starting material is not shown in thespectra). The shift was expected due to the different magneticenvironment after the reaction.

SEM image of purified SWNTs and 1,3-dipolar cycloaddition functionalizedSWNTs are presented in FIG. 6. Two different views of SEM images werepresented for both pristine SWNTs and functionalized SWNTs. The pristineSWNTs exist as bundles with 20 to 30 nm size in diameter, as shown inFIGS. 6(a) and 6(b). Before functionalization, the walls of the tubewere clean and smooth. SWNTs tended to aggregate into bigger bundlesafter the reaction, with typical diameter of 200 to 300 nm. These areshown in the spectra of 6(c) and 6(d). Because of the attachment ofamino acid and aldehyde, the wall the tube became rough as shown in FIG.6(d). However, the cylindrical shape of SWNTs is clearly observableafter functionalization. It is not possible to judge by the SEM if thefunctional groups were covalently attached to SWNTs. However, thesolubility of the material in the organic solvent, and the FTIR, H-NMR,and UV-vis data are decisive arguments in support of the covalentfunctionalization of SWNTs.

Example 2

This exemplary embodiment shows a method of synthesis of highly, waterand alcohol, soluble nanotubes, and in particular, SWNT. The experimentincludes utilizing a CEM Model 205 microwave oven with a typically 100ml or larger closed vessel reaction chamber, lined with Teflon PFA® andfitted with a 0˜200 psi pressure controller. The SWNTs used wereprepared by the high pressure HiPCO process.

In this embodiment, 10 to 20 mg of SWNTs were added to 20 ml of amixture of 1:1 nitric acid (70%) and sulfuric acid (97%) in the reactionchamber. The reaction vessel was then subjected to microwave radiation.The microwave power was set at 50% of a total of 900 watts, and thepressure was set at 20 psi. The microwave-induced reaction was carriedout for 1, 2, 3, 5, 10 and 20 minutes respectively. Three minutes wasfound to be the optimum reaction time. At this point, the functionalizedSWNTs became highly water soluble, and no nanotubes were lost. After thereaction, the reacted mixture was diluted with de-ionized (DI) water.Then the mixture was filtered through a 10 μm PTFE membrane paper, andthe filtrant was transferred to a dialysis bag (nominal MWCO12,000-14,000). When the pH reached 7, the diluted mixture was removedand concentrated in a vacuum evaporator. The resulting black SWNT solidswere used for testing solubility and for characterization. The spectrashown are from nanotubes that were reacted for 3 minutes.

Field emission SEM images were taken using a LEO microscope and the TEMusing a 200 kV LEO microscope. The infrared and Raman spectra wererecorded using a Perkin Elmer FTIR spectrometer and Horiba/Jovin YvonLab Ram system with 632.8 nm excitation, respectively. Thethermogravimetric analysis measurements were performed with a UniversalV3.7A instrument. The UV-vis-NIR spectra were obtained from HewlettPackard, Model 8453 UV-Visible spectrophotometer. The particle sizeanalysis was performed on a Beckman Coulter N4 Plus Submicron ParticleSize Analyzer.

Laser light scattering particle size measurements of the aqueoussolutions of microwave functionalized SWNTs were compared withmeasurements made on an aqueous suspension of pristine SWNTs. Thesuspension prepared by sonication of a mixture of 0.1 weight % and 0.5weight % of the surfactant Triton-X showed particle sizes ranging from100 nm to 600 nm with a peak at 300 nm at detection angles of 62.2 and90 degrees. In contrast, the aqueous solution of microwavefunctionalized SWNTs did not show the existence of particles in the 3 to800 nm size range, clearly indicating that these nanotubes dissolve inwater.

SWNTs deposited from aqueous solution generate scanning electronmicroscope (SEM) and transmission electron microscope (TEM) imagesdisplayed in FIGS. 8A and 8B, respectively. The SEM images indicateclear alignment of the depositing nanotubes resulting from capillaryforces during evaporation of the solvating water molecules. Alignment ofthe carbon nanotubes is seen each time after evaporation of a drop ofthe solution. The TEM image shows extensive debundling of the SWNTropes, but no indication of structural modification of the sidewalls canbe seen at this magnification level.

In order to characterize the chemical groups formed on the nanotubesidewalls and tube ends after microwave treatment, Fourier-Transforminfrared (FTIR) and Raman spectra of the functionalized SWNTs weremeasured and are shown in FIG. 9 FTIR spectra of the microwavefunctionalized SWNTs were obtained to determine the structure of thechemical groups formed on the nanotube sidewalls and tube ends. Likegraphite, the FTIR spectrum of the pristine nanotubes (FIG. 9Aa) ispractically featureless with extremely low infrared absorptionintensities. After the microwave-induced functionalization a typicalFTIR spectrum (FIG. 9Ab) showed a number of infrared lines, which wereassigned as follows: The line at 1719 cm⁻¹ was assigned to the C═Ostretching mode of the —COOH groups (where the carbon is from the SWNTbackbone) on the SWNTs, whereas the intense, broad line centered at 3422cm⁻¹ was assigned to the —OH stretching mode of the —COOH group. Theline at 1637 cm⁻¹ was assigned to the SWNT C═C graphitic stretching modethat is infrared-activated by extensive sidewall functionalization. Thestrong line observed at 1355 cm⁻¹ was assigned to the asymmetric SO₂stretching mode of the acid sulfonate (—SO₂OH) group, whereas the lowerfrequency line at 1200 cm⁻¹ was assigned to the SO₂ symmetric stretchingmode. The shoulder near 2600 cm⁻¹ was assigned to the —OH group of thesulfonic acid group. The FTIR spectrum is consistent with elementalanalysis of the functionalized SWNTs, which showed that one in threecarbon atom on the SWNT backbone was carboxylated, and one in ten wassulfonated. In addition, an FTIR spectrum taken in KBr (not shown here)showed a line of medium intensity at 592 cm⁻¹, which was assigned to theC—S stretching mode, thus implying that the acid sulfonatefunctionalization was covalent. In some samples, the presence of tracewater formed the hydrated sulfonic acid group, —SO₃—H+H₂O, which gaverise to a strong infrared line at 1114 cm⁻¹ assigned to the asymmetricstretching mode of SO₃, and a shoulder near 1000 cm⁻¹ assigned to thecorresponding symmetric stretching mode. The combination of extensivecarboxylation and acid sulfonation on the SWNTs resulted in chargetransfer-induced formation of an SWNT polyelectrolyte salt in thepresence of polar solvent molecules followed by dissolution via ionicdissociation.

In the Raman spectrum of pristine SWNTs (FIG. 9Ba, right panel), SWNTsof three different diameters are indicated by the peaks at 189 cm⁻¹, 213cm⁻¹ and 252 cm⁻¹ due to the SWNT radial breathing modes (RBMs). Thestrong tangential C—C mode is seen at 1578 cm⁻¹, and a weak line due todefects and disorder on the SWNT framework is observed at 1299 cm⁻¹.After three minutes of nitration, only the RBM line at 189 cm⁻¹associated with larger diameter SWNTs, is observed (FIG. 3Bb, right),suggesting that the smaller diameter SWNT were the first to befunctionalized. Compared to the Raman spectrum of pristine SWNTs thereis a 2 cm⁻¹ up-shift of the tangential mode frequency of the reactedSWNTs probably due to the attachment of electronegative groups, such as—COOH and —NO₂ to the SWNT backbone. Furthermore, the broad line in thedefect mode region of the spectrum broadens, shifts up in frequency anddramatically increases in intensity. This is due to the extensivenitration and carboxylation of the sidewalls and tube-ends resulting insp₃-hybridization and disorder on the nanotube framework. Part of thebroadening and up-shift can also be attributed to the appearance of thesymmetric stretching mode of the —NO₂ groups in the Raman spectrum. FIG.9Bc (right panel) shows the Raman spectrum of the functionalized SWNTsin aqueous solution—the first time such a spectrum has been obtained forSWNTs. Probably because of water solvation around the nanotube backbone,RBM modes are not observed and the tangential mode frequency is shiftedup in value by 15 cm⁻¹ relative to that of the functionalized solid.

Further characterization of the functionalized SWNT aqueous solutionswere performed using visible-near infrared (vis-NIR) absorptionspectroscopic measurements of the solutions and comparing a typicalspectrum to that taken from a suspension of pristine SWNTs indimethylformamide (FIG. 10A). Inter-band transition absorptionsassociated with the van Hove singularities in quasi-one dimensionalpristine SWNTs are clearly seen at 740, 820 and 890 nm in spectrum ofthe pristine SWNTs shown on the left panel of FIG. 4 a. Thecorresponding spectrum of the microwave functionalized solution isfeatureless, indicating a loss of the quasi-one dimensional SWNTstructure due to extensive functionalization of the sidewalls. Thedegree of nitration and carboxylation of the SWNT structure indicated bythe infrared and Raman data was quantified by thermogravimetric analysis(TGA) measurements on pristine and microwave functionalized SWNTsperformed under dry nitrogen at a heating rate of 10° C. per minute from30° to 500° C. The TGA traces shown in FIG. 4B indicate that compared topristine SWNTs, the functionalized SWNT lose about 50% of its weight dueto dissociation of the —NO₂ and —COOH groups from the nanotube backboneand tube ends. This would indicate that approximately every four carbonson the SWNT structure is functionalized by the microwave process.

As seen by this embodiment, in addition to its high solubility, aqueoussolutions of microwave functionalized SWNTs are electrically conducting,with conductivity in de-ionized water of 215.8 μS relative to that of1.5 μS for de-ionized water. This raises the possibility for electricalmanipulation (such as, electrodeposition) of the SWNTs from a solutionphase.

Example 3

This exemplary embodiment shows a method of synthesis of ceramic-SWNTcomposite. The experiment includes utilizing a CEM Model 205 microwaveoven with a typically 100 ml or larger reaction chamber, lined withTeflon PFA® and fitted with a 0˜200 psi pressure controller. The Fouriertransform infrared spectroscopy (FTIR) measurements were made either inhighly purified KBr pellets (solid sample), or on NaCl crystal window(liquid sample) using a Perkin Elmer instrument. The Raman spectra wereobtained using a Renishaw System 1000 Micro-Raman Spectrometer with 785nm laser as the excitation source. The transmission electron microscope(TEM) images were recorded using a TOPCON 200 kV Ultra-High ResolutionTransmission Electron Microscope. The scanning electron microscope (SEM)images energy dispersive X-ray (EDX) data were obtained using a LEO 1530instrument. Thin film X-ray diffraction (XRD) data were collected on aPhilips X'Pert MRD instrument equipped with an Eulerian Cradle, and witha Cu point source and Ni filter.

To reduce or eliminate residual metal catalyst and to generate —COOHgroups, the SWNTs were first treated in nitric acid solution for fewminutes under microwave radiation. In a typical composite formingreaction, about 10 mg of the pretreated SWNTs and 5 ml ofchlorotrimethylsilane were added to the microwave reaction vessel. Atthe same time, another 5 ml of chlorotrimethylsilane was used as thecontrol in a separate vessel. Both the vessels were subjected tomicrowave induced reaction for 10 minutes, with the power set at 75% ofa total of 900 watts, and the pressure set at 125 psi. Once cooled, theliquid in the control vessel remained clear, but a tree-like solidcomposite was observed standing in the reaction solution. It wascarefully removed from the reaction chamber, washed with chloroform,ethyl alcohol, and distilled water. After air drying over night, thecomposite weighed about 70 mg.

Under the reaction conditions presently disclosed, a gray-black solidwith a branched structure, as shown in the optical image in FIG. 11 aand FIG. 11 b, rapidly precipitated out of the fine suspension. Thecomposite was between 2 to 4 cm each in length, width and height. It wasprobably restricted by the size of the reaction vessel. The bulkstructure was strong enough to be handled manually. The reaction wasfound to be highly reproducible; a solid composite of similarmorphology, shape, color was obtained every time.

EDX analysis detected four elements in the composite: C, Si, O and Cl,with atomic compositions of 55%, 33%, 9%, and 3% respectively. Thisindicated a composite composition of 65% of SiC, 15% of SWNTs and 15% ofSiO₂ by weight, assuming that all the oxygen was incorporated in SiO₂.The relatively small amount of chlorine might have been absorbed fromthe chlorotrimethylsilane that remained after washing and drying. AnX-ray diffraction (XRD) scan of the composite was performed using anarea detector and a rotating anode x-ray generator equipped with agraphite monochromator (Cu Ka; 1=1.5418 Å). The composite was finelyground prior to running the XRD pattern. The presence of nanocrystallineSiC is clearly indicated by the XRD pattern displayed in FIG. 12, whichshows broadened (111), (220) and (311) reflections offace-centered-cubic SiC at 20 values of 35.6, 60.2 and 71.7 degrees,respectively. The presence of amorphous SiO₂ is indicated by a broadshoulder at a 20 value near 22 degrees.

The FTIR spectra of the starting material, the final composite and thechlorotrimethylsilane in the control vessel are shown in FIG. 13.Without the SWNTs, the chlorotrimethylsilane in the control vesselremained unchanged under microwave irradiation, and its spectrum wasidentical to that of the starting material, which is shown in FIG. 13 b.The FTIR spectrum from the nitric acid purified SWNTs is shown in FIG.13 a. The carboxylic (—COOH) groups generated during the purificationprocess gave rise to the line at 1730 cm⁻¹ due to the C═O stretchingmode. However, the COOH groups were absent in the composite as shown bythe spectrum in FIG. 13 c. A strong, relatively broad Si—C stretchingline was seen at 838 cm⁻¹. In addition, on comparing the spectrum ofchlorotrimethylsilane (FIG. 13 b) with that of the composite, it wasobserved that the C—H stretching mode lines at 2965 cm⁻¹ and 2902 cm⁻¹and the different Si—C stretching and rocking modes at 846 cm⁻¹, 760cm⁻¹ and 660 cm⁻¹, were absent in FIG. 3 c. This indicates the completecleavage of the SiC—H₃ bonds during the microwave reaction. The weakline at 1052 cm⁻¹ in FIG. 3 c also suggests the formation of smallamounts of SiO₂ in the composite. The presence of unreactedchlorotrimethylsilane in the control vessel indicated that the SWNTswere clearly involved in the formation of the SiC-SWNT composite. Theabsence of —COOH groups in the SiC-SWNT composite suggests that thereaction was initiated at these sites.

Part of the composite was uniformly ground for obtaining the Ramanspectrum shown in FIG. 14. The existence of SWNTs can be seen from boththe appearance of the radial breathing mode and the tangential mode ofthe SWNTs in the Raman spectra. As compared to the pristine SWNTs, theRaman spectra of SiC-SWNT showed a strong increase in intensity of thedefect or disorder mode, which most likely was due to the increasedsp₃-hybridization induced disorder on the nanotube framework afterfunctionalization. Some background fluorescence in the Raman spectrum ofthe composite was noted due to trace amount of absorbedchlorotrimethylsilane.

The SEM images in FIG. 15 provide insights into how the threedimensional architecture of the composite was formed. As indicated byFIG. 15 a and FIG. 15 b, the nucleation of SiC probably occurred on theSWNT sidewalls at the onset of the reaction. Then, the SiC particlesrandomly cross-linked as evident from FIG. 15 a and grew into themacroscopic architecture shown in FIG. 11. As shown in FIG. 15 c, incertain areas of the composite, the SWNTs were completely covered by theSiC spheres. The image shown in FIG. 15 d is from the surface of afractured region, and the nanotubes that formed the underlying frameworkof the composite structure are still embedded. This indicates stronginterfacial binding of the SWNTs to the SiC particles. The nanotubestherefore appear to reinforce the composite in a manner similar to steelin reinforced concrete. It is likely that the high tensile strength ofthe SWNTs prevented their breakage during fracture of the composite.

A small portion of the composite was ground and sonicated in methanolfor about 5 minutes. Then a drop of the suspension was cast onto the TEMgrid for measurements. The TEM image in FIG. 15 e shows that the SWNTswere debundled and randomly linked by SiC spheres, which are clearlyseen at the bottom of the image. A fine coating is observed on the SWNTsidewall in the magnified TEM image in FIG. 15 f. In addition, the SWNTsappeared to be cross-linked. Relatively few SiC particles are seen inthe TEM images because the grinding and sonication during the TEM samplepreparation removed some of the loosely held particles.

A proposed mechanism for the growth of the SiC-SWNT composite is shownin FIG. 16 a. The growth appeared to be initiated by the reaction of—Si(CH₃)₃ at the —COOH sites by forming HCl and CO₂. The methyl-silanethus formed was further decomposed by the microwave radiation to producerandomly growing SiC nanoparticles, which covered the nanotube surfaceand led to the formation of a heterogeneous SiC-SWNT network. Theprocess depicted in FIG. 16 b shows a layer of SiC chemically bonded tothe SWNT surface, onto which larger SiC spheres grew. The oxygen in thereaction chamber reacted to form small amounts of SiO₂, which can beetched away by dilute HF.

The embodiment of the invention as synthesized through the synthesismethod of the present invention is a high purity SiC-SWNT compositesynthesized through a novel, low temperature, microwave-induced approachas verified by the illustrated infrared and Raman spectroscopy, x-raydiffraction, and electron microscopy data. The synthesis reaction, whichwas completed in a matter of minutes, involved the nucleation of SiCdirectly on the SWNT bundles. Formation of multiwalled nanotubes andother carbonaceous structures usually seen in the reverse approach ofgrowing SWNTs in a ceramic matrix were not observed.

Although the invention is illustrated and described herein withreference to specific embodiments, the invention is not intended to belimited to the details shown. Rather, various modifications may be madein the details within the scope and range of equivalents of the claimsand without departing from the invention.

1. A method for rapidly functionalizing a nanomaterial, comprisingperforming a functionalization reaction wherein said functionalizationreaction comprises subjecting said nanomaterial and at least onefunctionalizing reactant to microwave conditions.
 2. The method of claim1 wherein said functionalization reaction is selected from the groupconsisting of carboxylation, sulfonation, esterification, thiolation,carbine addition, nitration, nucleophylic cyclopropanation, bromination,fluorination, diels alder reaction, amidation, cycloaddition,polymerization, adsorption of polymers, and addition of biologicalmolecules and enzymes.
 3. The method of claim 1 wherein saidfunctionalization reaction further comprises covalent bonding.
 4. Themethod of claim 1 wherein said functionalization reaction furthercomprises an amidation of said nanomaterial.
 5. The method of claim 1wherein said functionalization reaction comprises a 1,3-dipolarcycloaddition of said nanomaterial.
 6. The method of claim 1 whereinsaid nanomaterial is selected from the group consisting of single wallcarbon nanotubes (SWNTs), multiwall carbon nanotubes, carbon nanohorns,fullerenes, nano onions and nanocomposites.
 7. The method of claim 1wherein said nanomaterial comprises an SWNT.
 8. The method of claim 1wherein the reaction time of said functionalization reaction comprisesabout 1 second to about 30 minutes.
 9. The method of claim 1 whereinsaid nanomaterial is non-soluble prior to functionalization.
 10. Themethod of claim 9 wherein said functionalization reaction comprises asolubilizing reactant and wherein said functionalization reactionsolubilizes said nanomaterial.
 11. The method of claim 10, wherein thesolubilizing reactant is selected from the group consisting of aqueous,organic, polar, nonpolar and hydrogen bonding solvents.
 12. A method forrapidly generating a soluble, functionalized nanomaterial comprising afunctionalization reaction wherein said functionalization reactioncomprises subjecting non-soluble nanomaterial and at least onefunctionalizing reactant to microwave conditions.
 13. The method ofclaim 12 wherein said nanomaterial is selected from the group consistingof single wall carbon nanotubes (SWNTs), multiwall carbon nanotubes,carbon nanohorns, fullerenes, nano onions and nanocomposites.
 14. Themethod of claim 13 wherein said nanomaterial comprises an SWNT.
 15. Themethod of claim 12 wherein said functionalization reaction furthercomprises subjecting said nanomaterial to an acidic treatment.
 16. Themethod of claim 15 wherein said acidic treatment comprises a 1:1 mixtureof nitric acid and sulfuric acid in water.
 17. The method of claim 12wherein the reaction time of said functionalization reaction comprisesabout 1 second to about 30 minutes.
 18. A method for synthesizing ananomaterial composite comprising: providing a nanomaterial; adding atarget material selected from the group consisting of a ceramiccompound, a metal, a polymer, and combinations thereof, to saidnanomaterial, wherein the target material and nanomaterial combinationis exposed to microwave conditions to form said nanomaterial composite.19. The method of claim 18 wherein the target material comprises aprecursor of a ceramic compound, a polymer, or a metal.
 20. The methodof claim 18 further comprising the step of treating said nanomaterialwith a suitable amount of an acidic solution prior to combining withsaid target material.
 21. The method of claim 18 wherein the step oftreating said nanomaterial with a suitable amount of an acidic solutionfurther comprises exposure to microwave conditions for a suitableduration.
 22. The method of claim 18, wherein the ceramic compound isselected from the group consisting of carbides, borides, nitrides,suicides, barium titanate, bismuth strontium calcium copper oxide, boroncarbide, boron nitride, aluminum silicates, earthenware, Ferrite, leadzirconate titanate, magnesium diboride, porcelain, silicon carbide,silicon nitride, Steatite, uranium oxide, yttrium barium copper oxide,zinc oxide, zirconia, and combinations thereof.
 23. The method of claim18, wherein the metal comprises a salt.
 24. The method of claim 23wherein the salt is selected from the group consisting of LiAlH4. LiBH4;and CdS.
 25. The method of claim 18, wherein the polymer is selectedfrom the group consisting of methyl methacrylate, polyvinyl pyrrolidone,polyurethane, polyamide.